In a device including a PWM circuit, to ensure the device can work normally, a maximum duty cycle of a modulation signal output by the PWM circuit needs to be controlled (e.g., no more than 90%).
A gain defined by equation (1) is another important parameter for a PWM
                    Gain        =                  Duty                      V            ctrl                                              (        1        )            
Where Duty is a duty cycle of a modulation signal output by the PWM circuit, Vctrl is a voltage of a control signal provided to the PWM circuit.
Conventionally, a PWM circuit can have a controllable maximum duty cycle but not simultaneously a controllable gain. Controllable gain is needed to keep other components, e.g., a feedback loop, stable. Without stability, the feedback loop cannot generate desirable output signals.
Therefore, a PWM circuit with a controllable maximum duty cycle and gain is desirable.